Australia has deployed a large contingent of unarmed federal police to Ukraine’s second biggest city Kharkiv as it prepares to lead a security mission to secure the MH17 crash site.

More than 100 Australian Federal Police (AFP) officers flew into Kharkiv on Saturday, according to reports.

Some are believed to have gone in on the RAAF C17 Globemaster that has been used to shuttle bodies back to the Netherlands for identification.

The AFP officers joined some 40 plain-clothes military police from the Netherlands who are now expected to begin work escorting forensic experts to the crash site near Grabov.

Foreign Minister Julie Bishop will fly back to Kiev as Canberra pushes the Ukrainian government to ratify an agreement that would allow Australia to send in an additional, but smaller, contingent of armed police and soldiers to protect investigators.

While unarmed police can enter at the invitation of the Ukrainian government “in order to bring in arms it’s in their constitution you have to have parliamentary approval”, Ms Bishop told reporters in Eindhoven on Saturday.

The foreign minister has signed an in-principle deal with her Ukrainian counterpart, Pavlo Klimkin, that would allow Australia to lead an armed security mission.

But it still needs to be ratified by the parliament.

Getting the arrangement finalised has been complicated by the collapse of the ruling coalition and the resignation of Prime Minister Arseniy Yatsenyuk.

An extraordinary session is scheduled for Thursday, when the deal could be ratified, but Ms Bishop and her Dutch counterpart, Frans Timmermans, want the mission approved on Tuesday.

“We want our experts in there as soon as possible,” Ms Bishop said when asked if Australia could wait until Thursday.

“We want to be able to start retrieving the last of the remains on site as soon as possible and we want the investigation to commence as soon as possible.”

Ms Bishop said she and Mr Timmermans would therefore travel to Ukraine on Sunday to meet with senior Ukraine officials “to urge them to ratify our respective documents on Tuesday”.

“This is a significant request to have a parliament recalled after it went into recession on Friday.

“But last week we were assured that our documents would be ratified on Friday.

“Domestic politics and internal matters intervened so we are returning to ask if it’s possible for them to reconvene the parliament on Tuesday because every day that we are not on the site it becomes more contaminated.”

The foreign minister said while awaiting ratification Australia and the Dutch could “preposition and put our resources in place outside Ukraine ready to move as soon as possible”.